The invention relates to an implement hitch and a control system therefore.
The towing force between the utility vehicle and the implement may depend in particular on the sideways orientation of the implement relative to the utility vehicle. In August van der Beek: xe2x80x9cDie Lage des ideellen Fuehrungspunktes und der Zugkraftbedarf beim Pfluegenxe2x80x9d Grundlagen der Landtechnik (1983) Nr.1, s. 10-13 (xe2x80x9cThe Position of the Ideal Guide Point and the Towing Force Requirement During Plowingxe2x80x9d, Fundamentals of Agricultural Technology (1983) No. 1 page 10-13), a system was examined which consisted of an agricultural tractor with a plow coupled to a three-point linkage. The plow included a repositioning system for influencing the position of the three-point linkage and thereby to determine the position of the ideal guide point (towing point). The ideal guide point in this case results from the intersection of the extension of the pivotal two hitch links and determines orientation of the resulting forces between tractor and plow. The factors to be considered include, among others, track width, tire width, wheel base, front axle load as well as the number of driven wheels of the tractor, and the size, number, shape and operating width of the plow components. It was found that the towing force of a plow coupled to a tractor can be minimized if the ideal guide point is repositioned to the side of the furrow.
The coupling points of a plow are usually moved sideways relative to its frame by means of a coupling unit mounted on the plow, such as repositioning spindles described in DE-A-31 07 137, or hydraulic cylinders described in DE-A-196 39 573.
DE-A-196 39 573 describes a tractor with a plow coupled thereto via a conventional three-point linkage or hitch in which an optimum repositioning of the plow is to be attained by comparing the lower steering arm forces. For this purpose, the lower steering arm forces are measured by a separate force sensor. The relationship of the lower steering arm forces is used as a control value which is compared with a target value that can be provided by the operator. As a function of the difference, a double acting hydraulic cylinder is controlled to control the position of the plow and the hitch, in order to reposition the position of the ideal guide point for the line of action of the resulting forces between the tractor and the plow.
Hydraulic cylinders can control the width of the furrow and reposition the towing point. However, the plow must be equipped with its own control or regulating system. If a user wants to use several implements in connection with a utility vehicle, then he must invest in several control systems, which is costly. By varying the configuration of these control systems, the demands on the operator increase.
An object of the invention is to provide a hitch and a control system which solves the aforementioned problems.
In particular, an object of the invention is to provide a hitch and a control system which automatically, upon certain conditions, repositions the towing point and the line of action of towing forces and/or the operating width and the angle of inclination of the implement, without the need for each of the implements being provided with its own control system.
These and other objects are achieved by the present invention wherein a hitch couples an implement to a self-propelled utility vehicle, such as a tractor. The hitch includes adjustable length coupling elements and a coupling unit for coupling the implement to the hitch. The coupling unit pivots the implement freely (not controlled) relative to the utility vehicle, so that the implement can reposition itself in response to forces. A control system controls the length of the coupling elements in order to control the operating line of the draft forces, and/or the position of a towing point defined by the coupling unit, and/or an angle of inclination of the implement.
In contrast to the state of the art, the coupling unit can pivot freely in a horizontal plane within certain limits. The hitch is controlled to control position of implement relative to the utility vehicle. Thus, each implement need not be equipped with its own repositioning system. Rather, only a control system associated with the utility vehicle is required. This reduces cost and simplifies the operation because the operation of different control systems need not be learned.
With this hitch, the towing point can be repositioned automatically so that the operating line of the draft forces conform to the desired requirements, and to improve the transmission of the forces to the ground and reduce friction forces between the plow and the ground. This can reduce energy consumption by up to 15%. The torque about a vertical axis of rotation can be reduced, so that the operator is relieved of frequent counter-steering.
The hitch includes lower hitch links which are engaged at the sides by hydraulic cylinders, as is shown by EP-A-1 084 602. Preferably, the hitch includes six adjustable length coupling elements arranged in the form of a hexapod, such as described in greater detail in German patent application P-199 51 840 8, which is incorporated by reference herein.
The hexapod defines a coupling plane which defines a set of coupling reference positions, and can be controlled and moved actively and repositioned within a given operating region relative to the utility vehicle, particularly in a horizontal plane. The coupling unit defines a coupling plane associated with the implement which can be freely moved relative to the implement frame.
Preferably, position sensors sense the length of the coupling elements. The actual position of the coupling plane and the coordinates of the coupling points of the hitch can be determined from the sensed lengths.
Force sensors sense the tension and compression forces in the coupling elements to determine the magnitude and the direction of application or the line of action of the draft forces produced by the implement engaging the ground.
Preferably, the coupling elements support a coupling frame which includes coupling members, such as hooks (which define coupling points), for coupling the implement to the utility vehicle. A coupling carrier is coupled to the side of the implement and is mounted on the coupling points. Fixed coupling points on a coupling frame permit a simple and rapid coupling.
With a hexapod type hitch the implement can be moved in the longitudinal direction of the vehicle as well as upward and to both sides. It is also possible to rotate the implement about the longitudinal axis of the vehicle or to pivot it about a horizontal or vertical axis. However, only a limited rotation about a longitudinal axis is possible with the hexapod hitch. Therefore, a rotary mechanism is provided between the coupling frame and the coupling carrier of the implement, which permits rotation of the implement about a generally longitudinal axis. A sensor senses the rotational angle of the rotary mechanism.
When a plow is inserted into the ground, the plow does not immediately cut in the proper furrow width. A plow may also be forced out of its normal position by an obstacle, such as a stone or a root. For this reason the kinematics of conventional hitches have been designed to rapidly return a plow to its normal position after it has been displaced therefrom.
According to the present invention, however, the coupling elements of the hitch are not freely movable during an automatic repositioning of the towing point, so that their convergence has no effect upon the return movement. Preferably, the kinematics of the coupling unit conforms to the requirements of the convergence of the lower hitch links of the power lift.
Thus, preferably, the coupling unit includes a pair of horizontally spaced apart tie rods. The tie rods may be rigid hitch links which form a four-bar linkage coupled to the implement and to the coupling carrier and pivotal about vertical axis. Preferably, the tie rods convergence in a generally horizontal plane and are closer together in the direction of the utility vehicle. A point of intersection of the axes of the tie rods forms an ideal guide point or towing point.
If the hitch is slid to the side the coupling carrier rotates somewhat about a vertical axis depending on the convergence of the tie rods. The control system controls the hexapod hitch to rotate the coupling frame about a vertical axis by an amount which corresponds to the rotation of the coupling carrier. Thus, the coupling points may be shifted in a horizontal plane without changing the relative position between the utility vehicle and the implement.
This shifts the guide point or the towing point to the side. In case of a plow, the towing point can, for example, be repositioned to the side of the furrow so that the side forces acting on the sides of the plow are absorbed by the utility vehicle. With shifting the towing point further towards the side of the furrow, the side forces acting on the plow are reduced. If the line of action of the draft forces do not act through the normal axis of the utility vehicle, a torque about the normal axis develops. The torque increases with the deviation of the line of action from the normal axis. The increasing torque requires the operator to apply counter steering to an increasing degree in order to operate the vehicle through the furrow. Repositioning of the towing point from the normal axis of the vehicle to the side of the furrow reduces the friction forces and increases the torque. In a vehicle with pure rear wheel drive without a differential lock the normal axis can extend through the center of the rear axle.
In addition to length sensors for the coupling elements, a deflection angle sensor is used to determine the position or orientation of the implement relative to the coupling plane or the coupling carrier.
With this invention the direction of the line of action of the draft forces or the position of the towing point defined by the coupling unit and/or the angle of inclination between the utility vehicle and the implement can be conformed automatically to requirements.
However, during transport operation, an implement which is freely movable and rotatable in an uncontrolled manner may be bothersome or even dangerous. Therefore, a blocking means is provided through which the coupling unit can be selectively prevented from a sideways deflection and/or an inclination, particularly a rotation about the longitudinal axis of the vehicle. The blocking means includes a variable length element which is coupled to the implement frame and to the coupling carrier, and which can be fixed with respect to its length, such as a hydraulic cylinder controlled by a blocking valve. The hitch is controlled by a control system.
The control system includes a sensor arrangement that detects the relative position of the vehicle body (vehicle chassis, vehicle frame or some other reference point fixed to the vehicle) on the one hand and the implement frame on the other hand for a coupling reference system. The coupling reference system is defined, for example, by coupling or fastening points. It can, however, be defined by freely selected spacial parameters that lie in the region of the fastening planes. As an alternative or in addition to the detection of position the sensor arrangement can also detect the forces in the coupling elements that can be repositioned in length. Furthermore the control system contains control means that transmit control signals in order to automatically influence the length of at least one coupling element that is variable in length as a function of the sensor signals.
Preferably the control system generates control signals on the basis of the sensor signals and the vehicle and implement configuration by means of which the line of action of the resulting ground resistance and/or the position of the towing point defined by the coupling unit and/or the width of the furrow and/or the angle of inclination between the utility vehicle and the implement can be repositioned automatically in a pre-set manner directly or indirectly. In this way the front width of the furrow can be changed automatically, an automatic repositioning of the angle of inclination can be performed and/or the towing point can be repositioned automatically transverse to the direction of operation.